1. Field of the Invention
The invention relates to an intake airflow control mechanism for an engine, which includes a first valve shaft on which valve elements of intake airflow control valves are fitted in such a manner that the valve elements pivot in accordance with the rotation of the first valve shaft, a second valve shaft on which valve elements of intake airflow control valves are fitted in such a manner that the valve elements pivot in accordance with the rotation of the second valve shaft, an actuator that rotates the first valve shaft, and a link mechanism that transmits the rotation of the first valve shaft to the second valve shaft.
2. Description of the Related Art
Many types of engines such as cylinder-injection engines are provided with intake airflow control mechanisms that control intake airflows in cylinders such as swirl flows and tumble flows. The intake airflow control mechanism includes intake airflow control valves that are provided at intake ports of the engine, and opens and closes the intake airflow control valves to partially open and close the intake ports, thereby changing the manner of formation of the intake airflows in the cylinders.
FIG. 6 shows an example of an existing intake airflow control mechanism mounted in a V-engine. As shown in FIG. 6, the intake airflow control mechanism includes an actuator 50 that opens and closes an intake airflow control valves. Valve elements 53 of intake airflow control valves, which are provided at intake ports 52 for cylinders in one of the right and left banks of the V-engine (first bank), are fixed to a first valve shaft 51 in such a manner that the valve elements 53 pivot in accordance with the rotation of the first valve shaft 51. The base end of the first valve shaft 51 is connected to the actuator 50. The tip end of the first valve shaft 51 is connected to the base end of a second valve shaft 55 via a link mechanism 54, and the rotation of the first valve shaft 51 is transmitted to the second valve shaft 55 via the link mechanism 54. Valve elements 57 of intake airflow control valves, which are provided at intake ports 56 of cylinders in the other of the right and left banks (second bank), are fixed to the second valve shaft 55 in such a manner that the valve elements 57 pivot in accordance with the rotation of the second valve shaft 55
In the intake airflow control mechanism for a V-engine, when the actuator 50 rotates the first valve shaft 51, the rotation of the first valve shaft 51 is transmitted via the link mechanism 54 so that the second valve shaft 55 is rotated in accordance with the rotation of the first valve shaft 51. Therefore, even in a V-engine in which the valve elements 53 of the intake airflow control valves are provided at one of the right and left banks and the valve elements 57 of the intake airflow control valves are provided at the other bank, all the valve elements 53 and 57 are opened and closed with the use of only the single actuator 50. With the structure in which the first valve shaft 51 provided at one of the banks and the second valve shaft 52 provided at the other bank are connected to each other via the link mechanism 54, it is no longer necessary to provide actuators for the respective banks. As a result, the structure of the intake airflow control mechanism is simplified.
Japanese Patent Application Publication No. 2002-295271 describes a throttle mechanism for a V-engine, which is similar in structure to the intake airflow control mechanism for a V-engine described above. In the throttle mechanism, throttle valves are provided at intake ports of respective cylinders of a V-engine. Valve elements of the throttle valves provided at the banks are fitted on a first valve shaft and a second valve shaft in such a manner that the valve elements pivot in accordance with the rotation of the throttle valves. The first valve shaft and the second valve shaft are connected to each other via a link mechanism so that the first valve shaft and the second valve shaft rotate together with each other. Therefore, all the throttle valves, some of which are provided at the right bank and the other of which are provided at the left bank in the V-engine, are collectively opened and closed by a single actuator.
The above-described intake airflow control mechanisms for a V-engine are each provided with a sensor that monitors the operating state of the intake airflow control mechanism to determine whether a malfunction has occurred. Malfunctions that need to be detected include locking of a movable portion of the actuator 50, locking of the valve elements 53 and 57, and breakage of portions at which the operating members are connected to each other. In order to detect interruption of the driving linkage between the actuator 50 and the second valve shaft 55 due to, for example, breakage of a portion at which the link mechanism 54 and the second valve shaft 55 are connected to each other, the operating state of the second valve shaft 55 needs to be directly monitored. Therefore, the installation position of the sensor is limited. That is, a malfunction detection sensor 58 needs to be provided near the second valve shaft 55, as shown in FIG. 6. Accordingly, the actuator 50 and the sensor 58, which constitute an electric system of the intake airflow control mechanism, need to be provided at different locations. This increases the installation space, and makes it difficult to install the mechanism. If the workability during installation of the mechanism is taken into account, the actuator 50 and the sensor 58 are preferably integrated with each other. However, because the actuator 50 and the sensor 58 need to be installed at different locations, the structure in which the actuator 50 and the sensor 58 are integrated with each other cannot be employed.